It has long been known that fuels and chemicals can be obtained from coal. With the exception of the World War II period, however, when the European countries' petroleum supplies were interrupted, commercial exploitation of this knowledge has not been intensive: the lower cost of petroleum and the more highly developed technology for isolating industrially useful materials from it render coal a poor competitor with petroleum.
The recent large increase in the price of petroleum is tending to eliminate cost of raw material as a deterrent to the use of coal as source of fuels and chemicals: and, accordingly, focussing attention on improved techniques for recovering such materials from it.
Since coal cannot be employed for such purposes in the as-mined condition it must be converted to an intermediate to which recovery processes can be applied. The intermediate favoured in current industrial installations is tar, frequently obtained as by-product in the manufacture of smokeless solid fuel by low-temperature carbonisation of coal. The tar, however, represents a low proportion of the mass of the starting coal, and if the primary product of its production, namely smokeless fuel, is not of economic interest the resolution of the tar loses its attractiveness. Nevertheless, in the installations referred to the primary product has been of interest and the overall process, culminating with NaOH extraction of the phenols from the tar, has been economical. There have been proposals for the furthr refining of tar fractions, such as the removal of tar bases from the acids by sorption on a column of silica-alumina cracking catalyst described in U.S. Pat. No. 2,766,297.
The present invention is directed to a technique by which a far greater proportion of the original coal mass is resolved into useful products. To this end it employs as starting material such derivatives as solvent-refined coal which are obtained by methods involving the minimum possible carbonisation of compounds present in the coal. In addition, the resolution achieved is considerably sharper than have been previously achieved, thus increasing the quality as well as the quantity of product.